Waterproof adhesives and self-cleaning surfaces, mineralized teeth and hairy insect feet, the seemingly impossible-to-replicate awesomeness of spider silk: Here are a few of our favorite bio-inspired materials, and their natural sources.

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Sea Cucumbers: Shape-Shifters

Normally soft and squishy, aquatic sea cucumbers can become rigid and tough when threatened. This reversible transition, from pliant to stiff, inspired a team of scientists at Case Western Reserve University to design a material with similar properties. But first, they had to learn how sea cucumbers accomplish the transition: A network of collagen fibers, strung within a soft matrix, stiffens when the animal secretes chemicals that cause the fibers to form bonds.

The resulting biomimetic material transitions from stiff to soft when water is added. The nanocomposite is made of tiny cellulose fibers, strung in a rubbery polymer matrix, that form hydrogen bonds with the matrix until water is added, returning the compound to pliant form.

The team hypothesizes that such a material could one day be adapted for use in humans, as implantable neural electrodes, which need to be stiff during insertion, but flexible once in place.

Glass Sponge: Uncommonly Strong Glass Houses

Some deep sea sponges have skeletons made of a surprising material: glass. Appearing frail and ethereal, the sponges -- one of which is known as Venus' Flower Basket -- are anything but delicate. Their glassy skeletons are stronger than some cements, capable of sustaining the thousands of pounds of pressure present at the seafloor.

At Harvard University, Joanna Aizenberg has studied the molecular architecture that not only makes glass sponges so incredibly strong, but also allows them to harness minuscule amounts of light produced by undersea bioluminescent bacteria. Sponge building blocks are arranged in lattice-like structures -- the same type of design used by civil engineers, just much, much smaller. And the glass is layered, making it stronger, and capable of transmitting light.

Elsewhere, other scientists are also using sponges as a model -- or rather, the sponges' long, mineralized structures called spicules. On Mar. 15 in Science, a team of scientists from Germany reported the construction of a biomimetic spicule -- a long, flexible appendage made from calcite nanocrystals.

Photos: 1) Venus’ flower basket, a deep-sea sponge, is made of natural glass, each strand of which is composed of bundles of threads embedded like reinforced concrete. Each square window measures about 2 x 2 millimeters. Joanna Aizenberg/Wyss Institute 2) A closeup of the skeleton of the Euplectella, revealed by electron microscopy. These layers of natural glass fibers add strength and conduct light from the environment, serving both a mechanical and an optical function. Joanna Aizenberg/Wyss Institute

Chiton Teeth: Superstrong

Chitons are marine molluscs. One species, Chaetopleura apiculata, uses a crazy-looking array of teeth (pictured above) to chew up rocks and extract delicious algae. Derk Joester of Northwestern University is using the critter's odd, self-sharpening and bulbous teeth as a model for materials that could be used to form better artificial bone. He and his colleagues have studied how organic proteins can direct and support the growth of inorganic, bony tooth minerals, and are now studying crystal growth in sea urchins.

Another scientist, David Kisailus of the University of California, Riverside, is studying a different chiton's tooth. The gumboot chiton, largest and most meatloaf-like of the molluscs, has an array of teeth (below) shaped somewhat differently than its cousin's. But it, too, grinds up rock. Kisailus has found that gumboot chiton teeth contain magnetite, a mineral that makes them not only super-strong, but also magnetic.

After studying the process by which magnetite is incorporated into chiton teeth, Kisalius began working on developing a similar mineralization process for materials used in solar cells and lithium-ion batteries -- and, perhaps, body armor.

Mussels: Superglue

Despite the constant turbulence of tides, mussels manage to stay attached to their slippery, rocky homes. Their secret is a massively strong, sticky adhesive -- now the target of scientists hoping to replicate it.

The bivalves secrete proteins in a goopy form that solidifies into a thread-like water-resistant adhesive. Along its length, the thread is protected by protruding, knobby proteins that are mixed with iron. Proteins poking out of the leading edge of the sticky mix contain a high percentage of a particular kind of amino acid, called dihydroxyphenylalanine, which allows the mix to dry quickly and stick to slippery surfaces. Now, scientists have incorporated this amino acid into existing biomimetic mussel glues, and are testing the materials' ability to seal fetal membranes and arteries, and stick to places that superglue otherwise doesn't.

In February, scientists discussed mussel glue at the annual meeting of the American Association for the Advancement of Science. There, they considered the environmental stressors that can weaken mussel adhesion, ways to improve existing synthetic mussel-materials, and the potential roles for bioglue in such things as drug-delivery agent and surgical wound repair.

Lotus Leaf: Superhydrophobic

Instead of being absorbed, water droplets on a lotus leaf contract into balls -- the result of water's high surface tension and the leaf's bumpy, water-repellent surface. In addition to being hydrophobic, lotus leaves are also self-cleaning -- the perfect model system for things like exterior house paint, spray-on coatings, and fabric shields.

The lotus leaf has also inspired a coating that can be applied to silicon photovoltaic cells, designed by researchers at the Georgia Institute of Technology. Pyramidal shapes are etched into the silicon using various acids and nanogold particles, which control the size of the resulting bumps -- bumps that mimic the lotus leaf's rough surface.

As a result, the cells stay cleaner and absorb more light -- which is a good thing, if you're a plant leaf or solar cell.

Spider Silk: Superpowered

Like the superhero and associated arachnid, spider-silk possesses some pretty sweet powers. Super-stretchy and water-resistant, spider silk is also sticky, though spiders can safely crawl across it without getting stuck. It's light enough to hang effortlessly from trees and bathroom corners, and though most varieties are stronger than steel, there is at least one type of silk strong enough to stop trains.

Scientists have been trying to make synthetic spider silk for years. But whether grown in the lab, from genetically altered bacteria, or genetically altered goats, the artificial stuff just isn't as good as the real deal.

Yet.

Now, a company called AMSilk claims to have made the strongest synthetic version yet. Called Biosteel, the silk is produced by E.coli -- though the company won't disclose their manufacturing process. They hope to use the synthetic silk as a coating for surgical implants and products. Other hypothetical applications for synthetic silk include armor and solar sails -- and saving your city from real-life villains.

Burr Hooks: Superclingers

In the 1940s, Swiss engineer Georges de Mestral and his dog returned home from an Alpine hunting trip covered in burrs. After busting out his microscope, de Mestral realized that tiny hooks on the burrs allowed the seeds to cling to clothing and fur -- and basically anything that had a loop on it. The hitchhiking seeds and their tiny hooks inspired the engineer to design a similar, synthetic system that could reversibly bind two things together.

And thus, Velcro was born.

Today, the superstrong fastener is pretty much ubiquitous. It doesn't melt, it isn't undone by water, and it's strong enough to support about 80 pounds per square inch. Now, de Mestral's loops-and-barbs are found everywhere from shoes to upholstery, auto interiors, to space shuttles, and on people who fling themselves at walls.